Liquid development apparatus

ABSTRACT

A liquid developer is contained in a receptacle and a carrier having a latent electrostatic image thereon is guided through the liquid developer together with a development electrode for a distance sufficient to give a developed image of optimum density. In the several embodiments of the invention disclosed and described, the carrier is maintained in spaced relation to the development electrode and both are moved substantially in synchronism so that the developer therebetween is moved therewith at substantially the same linear speed as the carrier. By this arrangement with which the liquid developer is moved, a high degree of density uniformity and solid area coverage is obtained to provide an image of optimum density.

United States Patent [72] Inventors William Trachtenberg;

Gene H. Robinson; Orville C. Rodenberg,

Rochester, N.Y. [21] Appl. No. 739,326 [22] Filed June 24, 1968 [45]Patented Jan. 19, 1971 [73] Assignee Eastman Kodak Company Rochester,N.Y. a corporation of New Jersey [54] LIQUID DEVELOPMENT APPARATUSPrimary Examiner-Morris Kaplan Attorneys-William H. J. Kline, Robert F.Crocker and Lloyd F. Seebach ABSTRACT: A liquid developer is containedin a receptacle and a carrier having a latent electrostatic imagethereon is guided through the liquid developer together with adevelopment electrode for a distance sufficient to give a developedimage of optimum density. [n the several embodiments of the inventiondisclosed and described, the carrier is maintained in spaced relation tothe development electrode and both are moved substantially insynchronism so that the developer therebetween is moved therewith atsubstantially the same linear speed as the carrier. By this arrangementwith which the liquid developer is moved, a high degree of densityuniformity and solid area coverage is obtained to provide an image ofoptimum density.

PATENTED mu 9 I9?! SHEET 2 BF 2 DEVELOPER 1 REPLEN/SHER WILL/AMTRACHTENBE/il GENE H. ROB/NSOA ORV/LLE C. RODENBERC INVENTORS %4 fiz w 1LIQUID DEVELOPMENT APPARATUS FIELD OF THE INVENTION DESCRIPTION OF THEPRIOR ART It is well known in the prior art to apply a liquidcomposition to the surface of a movable web of material by means of asaturated pad that is held in contact with the material, or by means ofa cylindrical surface which carries a liquid composition from areservoir to the surface of the material on which the liquid compositionis to be applied. In each of such applicator arrangements, a pressureroll is usually necessary for maintaining the web of material in contactwith the pad or cylindrical surface. It is also known in the field ofxerography to move a web or carrier having latent electrostatic imagesthereon over an applicator, the liquid developer being applied underpressure against the surface of the carrier bearing the images. with anyone of the aforementioned arrangements the liquid composition is oftenapplied nonuniformly and/or with streaks which can vary in thickness.

In the field of xerography, the development of a latent electrostaticimage on the surface of a photoconductive material can be accomplishedby a process referred to as liquid development. This process uses adeveloper comprising an insulating liquid carrier in which charged tonerparticles are dispersed uniformly. In order to provide an optimum image,it is necessary that the toner particles be deposited uniformlythroughout the image areas, thereby providing a legible image of uniformdensity. Such results have been attempted by the prior art through theuse of a toner roller in a liquid developer followed by a set ofsqueegee rollers, a magnetic brush submerged in a liquid developer forachievingsolid uniform area development, application of a liquiddeveloper to a continuous web of film, as well as plate applicators ofthe type mentioned above.

In all of the aforementioned devices for developing an electrostaticimage by means of a liquid developer, the amount of toner in thedeveloper can decrease to the point where the carrier has very few, ifany, toner particles left for transfer to the material before beingseparated therefrom. As the rate of the development increases, that isthe rate of movement of the xerographic material increases, thedevelopment efficiency falls off considerably rather than increasing.Since the spacing between the developer head and the image-bearingsurface is very small, the developer liquid therebetween is easily andvery quickly depleted of its toner particles. Another disadvantage ofthe developing devices mentioned above is the production of flow streaksin the finished print due to the depletion of the toner particles ortheir being collected at some downstream site. It is therefore desirableto provide a liquid developer device which will provide a developedimage of maximum uniform density with no background deposits or flowstreaks and which will give such results with a relatively high rate ofmovement of the carrier through the liquid developer.

.SUMMARY OF THE INVENTION are usually prevalent when a carrieris drawnover an applicator or through a liquid developer.

Still another object of the invention is to provide a device for theliquid development of latent electrostatic images on a carrier in whicha development electrode is movable with the carrier andmaintained in afixed spaced relationship thereto and is also movable in synchronismwith the carrier through the developer'at a relatively high linearspeed.

And yet another object of the invention is to provide a device for theliquid development of latent electrostatic images on a carrier which isat least partially immersed in the liquid developer and by which theliquid developer between the carrier and a movable development electrodein the developer is moved at substantially the same linear speed as thecarrier.

A Other objects and advantages of the invention will be apparent tothose skilled in the art' when the more detailed description thereof isread in conjunction with the accompanying drawings. I

The above objects of the invention are attained by a device comprisingmeans for moving a carrier through a liquid developer in spaced relationto a developer electrode. The liquid developer is contained in areceptacle and the carrier is guided through the liquid developertogether with a development electrode for a distance sufficient to givea developed image of optimum density. In the several embodiments of theinvention disclosed and described hereinafter. the carrier is maintainedin spaced relation to the development electrode and both are movedsubstantially in synchronism so that the developer therebetween is movedtherewith at substantially the same linear speed as the carrier. By thisarrangement with which the liquid developer is moved, a high degree ofdensity uniformity and solid area coverage is obtained to provide anoptimum density image. Further, since the liquid developer is moved withthe carrier, the resulting developed image is free of any development orflow streaks.

DESCRIPTION OF THE DRAWINGS Reference is now made to the accompanyingdrawings wherein like reference numerals designate like parts andwherein:

FIG. 1 is a vertical sectional view through one embodiment of a liquiddeveloper apparatus in accordance with the invention;

FIG. 2 is a vertical sectional view taken along line 2-2 of FIG. 1 andshowing the structure of the drum for supporting the carrier and thedevelopment electrode;

FIG. 3 is a vertical sectional view through another embodiment of aliquid developer apparatus in accordance with the invention in which thelength of the development path has been increased; and

FIG. 4 is a vertical sectional view through still another embodiment ofthe invention in which the length of the development path is determinedby the spacing of several separate sets of drums and which discloses asystem for drying the carrier after development of the image.

DESCRIPTIONOF THE EMBODIMENTS OF THE INVENTION With reference to FIGS. 1and 2, a web or carrier 10 comprises a length of xerographic materialhaving a photoconductive layer which hasbeen exposed and bears a latentelectrostatic image. Such image is on the surface 11 of the carrier 10.A liquid developer 12 is contained in a receptacle 13 in which a drum 14is rotatably mounted. Drum 14 comprises a core 15 and can be providedwithflangcs 16 secured to said core as shown in FIG. 2. Core 15 isrotatably supported on a shaft 17 that is journaled in an extension 18fixed to each of sidewalls 19 of receptacle 13. By means of a nut 20 andpacking material 21, core 15 is scaled so that developer 12 cannot leakpast shaft 17. Core 15 can be a conductive material, such as stainlesssteel, a plastic material, or a plastic material with its peripheralsurface 22 covered with a metallic sleeve 23, as shown in FIG. 2.Flanges 16 can be of a metallic or a plastic material and provided witha shoulder 24 for supporting carrior 10. It may be necessary toelectrically insulate core from flanges 16 if both are made of anelectrically conductive material. As shown in FIG. 2, the width of thecore 15 and the distance between the flanges 16 can be varied toaccommodate any width of carrier 10. Also, the diameters of core 15 andshoulders 24 can be of a size as determined by the length of path andelectrode spacing necessary to obtain proper development of the images.Carrier 10 is guided by an electrically grounded roll 25 for entry intoliquid developer 12 and engagement with shoulders 24 of flanges 16. Onleaving liquid developer 12 in receptacle l3, carrier 10 moves over anelectrically grounded drive roll 26 which is driven by means of a motor27 and a suitable coupling arrangement designated by the numeral 28. Asdrive roll 26 is rotated, carrier 10 causes drum 14 to rotate due totension exerted thereon and the friction between the carrier and flanges16. Both grounded rolls act to make electrical contact with theconducting layer of the web. At this point, it should be noted that theimage bearing surface 11 of carrier 10 faces core 15 or sleeve 23 whichserves as a development electrode. Drum 14 is substantially immersed inthe liquid developer. Since the drum 14 and the carrier 10 are moved insynchronism, the liquid developer between the sleeve 23 and the surface11 of the carrier is moved with the carrier and drum at substantiallythe same linear speed. The sleeve 23, or core 15 if it is madeconductive, can be connected to a DC power supply 30 or grounded toprovide solid area development. If the core 15 is of an insulatingmaterial and power supply 30 is disconnected, then fringe development ofthe images will result. The liquid developer 12 can be replenished froma reservoir 31 which can be manually operated or automatically operatedin response to developer concentration and/or level. The distancebetween the peripheral surface of sleeve 23 or the core 15 and thesurface 11 of the carrier 10 can be between 0.0050.l50 inch, a distanceof 0.020'O.1OO inch providing an optimum spacing.

A strip of mm-wide xerographic material that was charged and contactexposed to a negative master was developed by the apparatus shown inFIG. 1. After development, the images were dried and fixed. Using thedeveloping apparatus just described, images resulted which were free ofstreaking and trailing effects. Uniformity of development was very goodand the maximum achievable density was about 2.00. The resolutioncapability of the developing unit was above 350 lines per millimeter andthe spacing between the image surface and the electrode was about 0.080inch.

With respect to FIG. 3 is a plurality of drums 40, 41 and 42 arearranged substantially as shown in a receptacle 43 filled with a liquiddeveloper 44. The drums 42 are substantially the same in structure asthe one disclosed and described with respect to FIGS. 1 and 2. However,in place of a sleeve, an endless belt 45 is used as the developmentelectrode and engages the peripheral surface of the core of each drum.Carrier having electrostatic images on the surface 51 thereof isthreaded over the electrically grounded guide roll 52 and held therebyin contact with the drum 40, around the drums 41 and 42, again intocontact with drum 40 with which it is held in contact on the oppositeside by the position of electrically grounded drive roll 53. The driveroll 53 is driven by a motor 54 which can also be connected through asuitable coupling 55 to one of the drums 4042. A DC supply 56 isconnected to one of the drums 4042 or to the belt 45. Also, a developerreplenisher 57 can be provided for use as described above with respectto FIG. 1.

In the arrangement disclosed in FIG. 3, a longer development path isobtained with a constant size gap being maintained between the belt 45and the carrier 50. The effective path length can be varied by changingthe relationship of the drums 4042, or by changing the level of theliquid developer. Also, the gap between the photoconductor and theelectrode can be changed by using flanges having a shoulder of therequisite diameter. By charging and exposing and then developing a stripof photoconductive material by the a paratus disclosed in FIG. 3, it wasfound that a maximum density of 1.3 resulted and characteristics ofuniformity of development and freedom from streaking and trailing wereas evident as in the embodiment disclosed in FIG. 1.

Another embodiment of the invention is disclosed in FIG. 4. in which aset of rolls 70 and 71 guide and move a carrier 72 through a liquiddeveloper 73 in a receptacle 74. In this embodiment, the carrier 72 isarranged with its surface 75, which bears the images, facing outwardlyand toward a development electrode 76. A second set of rolls 77-78 isarranged in receptacle 74 and completely immersed in the liquiddeveloper 73. The development electrode 76 comprises a flexiblestainless steel belt which encompasses the rolls 77 and 78. In thisarrangement, the rolls 77 and 78 are conductive and connected to a DCsupply 79. On the other hand, rolls 70-71 are held at ground potentialat all times. A motor 80 is connected through a suitable coupling 81 toone of the rolls 70 or 71 and 77 or 78 to provide means for moving thecarrier 72 and the belt 76 in synchronism. Since the rolls 7071 are alsoat least partially immersed in the liquid developer 73, the liquiddeveloper between the surface 75 and the electrode 76 is moved atsubstantially the same rate of speed as these elements. A developerreplenisher 82 is provided as in the previously-described embodiments.The length of the development path can be varied by making one of therolls 70, 71 adjustable relative to the other in the direction of thepath length, preferably, the roll that is not driven as roll 70 in FIG.4. By spacing the rolls 77, 78 at a maximum distance relative to thelength of the receptacle, the roll 70 can be adjusted to provide quite arange in path length.

The embodiments of the invention described hereinabove can be operatedwith carrier movement of 20 feet to 150 feet per minute. This range ofspeed of carrier movement for development of the image thereon isconsiderably greater than that attainable by any of the prior artdevices. Also, by making drums 14 and 4042 of insulating materials andmaking belts 45 and 76 of insulating materials, the images can be fringedeveloped. In any case, the developed images are free from streaking andtrailing due to the movement of the carrier through the liquiddeveloper.

As shown in FIG. 4, the carrier 72 can be dried at a high rate of speedwhen subjected to a vacuum knife 83, an air knife 84 and a heated drum85 or a heat gun 86, such elements being arranged beyond the receptacle74 in the direction of carrier movement and constitute means forremoving liquid developer from the carrier and drying the same. Forgreatest efficiency, the vacuum knife 83 is oriented generallyperpendicular to the plane of the carrier 72 and as close to thereceptacle 74 as possible. On the other hand, the air knife 84 is tiltedat an angle of 3045 with respect to the plane of the carrier 72 and hasits discharge opening about only an inch away from the vacuum knife 83.It has been found that the vacuum knife 83 will remove about 50-6Opercent of excess liquid as the carrier passes beneath it. Air knife 84then effectively pushes back most of the liquid that has escaped vacuumknife 83. The carrier is about 95 percent dried when it passes the airknife 84. The remaining moisture is completely removed by means of acontinuous blast of heat from the gun 86, or by means of the heated drum85.

One of the important advantages of the development techniques describedabove with respect to the several embodiments of the invention is thatthe final tonal sense of duplicates can be chosen independently of thetonal sense of the original images. The reason for this is that thedesign comprises an electrode that can be grounded or biased. Since thevolume of liquid developer carried between the carrier and electrodesurfaces is moved at about the same speed as the carrier, so that littleor no differential velocity exists between the carrier and thedeveloper, streaking and trailing of the images is eliminated. Theembodiments described represent an improvement over the units where thecarrier is pulled through a stationary liquid. In such apparatus thetoner particles can be easily removed or displaced from their originalsites due to the friction between the toner particles and the liquiddeveloper. In the present invention there is no relative motion betweenthe carrier and the developer, so that any external forces that couldeffect the position of the toner particles is eliminated.

The invention has been described in detail with particular reference topreferred embodiments thereof, but it will be understood that variationsand modifications can be effected within the spirit and scope of theinvention.

We claim:

1. Apparatus for developing a latent electrostatic image on one surfaceof a carrier, comprising:

a receptacle containing a liquid developer;

at least one drum having a peripheral electroconductive surface and apair of spaced, dielectric flanges for supporting said carrier formovement with said one surface in spaced relation to at least theportion of said peripheral surface that is immersed in said liquiddeveloper;

a source of electrical potential connected to said electroconductivesurface; and

means for moving said carrier and said drum in synchronism, whereby theliquid developer between said one surface and said peripheral surface ismoved with and at substantially the same linear speed as said carrier.

2. Apparatus for developing a latent electrostatic image on one surfaceof a carrier, comprising:

a receptacle containing a liquid developer;

a plurality of drums interconnected by an endless, electroconductivebelt for establishing a path of movement for said carrier;

said carrier being maintained by said drums with said one surface inspaced relation to at least the portion of said belt immersed in saidliquid developer;

each of said drums comprising a central hub for engaging said belt and apair of spaced, dielectric flanges for supporting said carrier in spacedrelation to said belt;

the hub of at least one of said drums being electrically conductive;

a source of electrical potential connected to said belt; and

means for moving said carrier and belt substantially in synchronism,whereby the liquid developer between said one surface and said portionof said belt is moved with and at substantially the same linear speed assaid carrier.

2. Apparatus for developing a latent electrostatic image on one surface of a carrier, comprising: a receptacle containing a liquid developer; a plurality of drums interconnected by an endless, electroconductive belt for establishing a path of movement for said carrier; said carrier being maintained by said drums with said one surface in spaced relation to at least the portion of said belt immersed in said liquid developer; each of said drums comprising a central hub for engaging said belt and a pair of spaced, dielectric flanges for supporting said carrier in spaced relation to said belt; the hub of at least one of said drums being electrically conductive; a source of electrical potential connected to said belt; and means for moving said carrier and belt substantially in synchronism, whereby the liquid developer between said one surface and said portion of said belt is moved with and at substantially the same linear speed as said carrier. 